Generally, in producing flat panels such as glass panels for use in an FPD (flat panel display) such as LCDs, touch panels, etc., a process of cutting a large raw material panel into flat panels having a desired size while taking productivity into account is essential. Such a panel cutting process includes a panel scribing process.
The scribing process is typically used in manufacturing a variety of display panels, semiconductor wafers, etc. using flat panels. In detail, the scribing process includes forming a scribing line, corresponding to the size of a flat panel to be produced, on a raw material panel, which is a scribing target to be cut. The target panel on which the scribing line has been formed is cut along the scribing line by applying force to opposite sides of the target panel based on the scribing line.
Typically, flat panels used in display panels, wafers, etc. are made of a brittle material such as glass or the like. Such brittle material is characterized in that when external force is applied thereto, the growth of a crack is very fast. Therefore, the scribing process is very useful in cutting such a brittle material.
Scribing wheels, which are generally used in such a scribing process, include a cutter part which has a plurality of fine recesses and a plurality of cutting blade teeth which are arranged along a peripheral edge of a wheel body. Such a scribing wheel generally has a similar shape to that of a circular saw.
The quality of a scribing process using the scribing wheel is determined depending on the structure of the recesses and the cutting blade teeth of the cutter part formed on the peripheral edge of the scribing wheel. Given this, research and development on the structure of the recesses and the cutting blade teeth of the cutter part are continuously being conducted.
FIGS. 1a and 1b are views showing an example of a conventional scribing wheel. As shown in these drawings, the conventional scribing wheel 101 is configured such that recesses 121 and cutting blade teeth 127 of a cutter part 120 are formed along a peripheral edge portion of a wheel body 110 having a circular shape. Generally, as shown in FIG. 1a, each recess 121 may have a V shape or, as shown in FIG. 1b, each recess 121 may have a U shape.
However, in the conventional scribing wheel, due to the structure of the recesses, when the cutter part cuts into a raw material panel such as a glass panel, which is a scribing target 130, as shown in an enlarged view of FIG. 2, corners C formed between the recesses and the opposite side surfaces of the peripheral edge portion of the wheel body come into contact with the scribing target. Thus, the area of a portion of the scribing target on which stress is concentrated is greatly increased in X- and Y-axial directions, whereby cracks k are caused in directions between the X- and Y-axial directions.
Consequently, cracks are formed in a significant surface area of a flat panel obtained through a scribing process. As a result, the strength, particularly, the bending strength, of the flat panel is markedly reduced.
Furthermore, as stated above, because the area of a portion of the scribing target on which stress is concentrated is greatly increased in X- and Y-axial directions due to the structure of the recesses of the scribing wheel, relatively large cracks are formed in side surfaces of the flat panel produced through the scribing process.
Therefore, the flat panel produced through the scribing process is typically machined through a side surface grinding process to remove cracks that remain in the side surfaces of the flat panel. Taking the side surface grinding process into account, the scribing process must be conducted after an extra area has been ensured on the peripheral side surfaces of the flat panel. However, these cause problems of an increase in material consumption and a reduction in productivity because of addition of the side surface grinding process.
That is, the cutter part including the recesses and the cutting blade teeth is formed along the cutting edge of the scribing wheel. If the recesses formed in the cutter part have a V or U shape in which they are recessed from only the cutting edge of the wheel, large cracks are caused around the vertexes of the cutting blade teeth.
In an effort to over the above-mentioned problems, as shown in FIGS. 3a and 3b, scribing wheels which include a cutter part having recesses each of which has grooves that are radially formed in respective opposite inclined surfaces of a periphery of the scribing wheel and meet at a cutting edge of the scribing wheel were introduced. In such a structure, the grooves formed in the opposite side inclined surfaces make discharge of glass chips easy. Improvement in the shape of a scribing line formed on a panel by the cutting blade teeth enhances the quality of cutting and the quality of edges of the cut panel. However, because the width of each recess ranges from 20 μm to 40 μm and the depth thereof ranges from 6 μm to 12 μm, it is difficult to use such a scribing wheel in cutting a thin panel for mobile devices.
Furthermore, recently, as interest in mobile terminals and tablet PCs, which have relatively large screens, is increased, improvement in the bending strength of display panels of mobile devices has been required to enhance the reliability of products. However, if the above-mentioned conventional scribing wheels are used to manufacture flat panels for use in display panels for mobile terminals and tablet PCs, the bending strength of products cannot be satisfied because of the above-mentioned problems.
Particularly, in manufacturing flat panels for use in display panels for mobile devices, the process of grinding the side surfaces of flat panels after the scribing process is generally omitted in consideration of the problem of the productivity. In this case, it is difficult to satisfy the desired bending strength.